I've a installation with a wireless guest network using NAC guest portal and from the VERY limited information that I've received it sound like that the clients get an error message in the web browser for the NAC portal redirect.
My colleague is onsite tomorrow but in the meantime I've checked the controller log and it's full of....
09/23/15 22:15:43 Major Security Manager Get next available session tracking tag (token) returns zero. Will not be able to process Captive portal authentication request.
So looks like they could be right and the ECP isn't working.
Is that a know issue which is fixed - I haven't found any information about such error.
If there is no fix release my plan is to just reboot the EWC.
V2110 - v9.15.01.0121
Netsight - v188.8.131.52